Dish-Stirling solar thermal power generation has the highest optoelectronic conversion efficiency among the solar thermal power generation technologies. It is suitable for small distributed energy system due to its relatively low power output. This system uses a parabolic concentrator to collect solar radiation and reflect it to the focal point of the concentrator, and the Stirling engine is usually placed near the facula of the focal. The concentrated high-temperature high-heat-flux-density heat is absorbed by heating tubes of the Stirling engine to heat the working gas inside. Thus, the solar energy is converted into thermal energy, ensuring the stable operation of the Stirling engine, and driving the generator to generate electricity.
The Stirling engine (also known as heat engine) is an engine that can realize reversible cycle by utilizing external thermal sources, i.e. engine based on Stirling cycle. It can be a piston engine which converts thermal energy to mechanical work taking advantages of the periodic expansion and compression of the working gas sealed in the circuit. The external heating characteristics of the Stirling engine bring a prominent advantage of energy adaptability. It can burn not only fossil fuels such as coal, gasoline, diesel, and natural gas, and biomass such as wood chips, straw, alcohol, and biogas, but also low-grade energy such as exhaust heat and solar energy. The external combustion process is continuous and thus easy to control combustion and realize complete combustion, so emission of harmful gases can be greatly reduced. In addition, the engine does not have knock and exhaust wave phenomenaso that the engine can be operated smoothly and reliably. The Stirling engine can be used as the prime mover of power generation, refrigerator, heat pump and pressure generator. Therefore, it has a wide application in appliances, automobiles, ships, aerospace, microelectronics, biological cryopreservation, etc.
The Stirling engine includes five parts, i.e. a cooler, a heater, a regenerator, a compression chamber, and an expansion chamber. The working gas will reciprocate in the circuit under the drive of pistons, and be heated by an external thermal source in the heater and cooled by an external cold source in the cooler. With different heating methods, the corresponding structures of Stirling heater are different. According to the relevant researches, the heat tube heated by fuel gas is generally a U-shaped straight tube. The heater is composed of a certain number of heat tubes which have circumferentially balanced arrangement. A radiation energy conversion device, which can heat corresponding working gas through specific wavelength of radiation, is equipped on the wall of the heat tubes, to improve the heat absorption of gas. When the solar radiation is weak, hot gas can be supplemented to perform convective heat transfer with the heat tubes. The heat tubes of solar radiation heated Stirling engine are usually designed to be an outstretched and totally symmetrical structure in order to absorb more solar energy within a limited space. In addition, there is an adiabatic cavity structure surrounding the heat tubes to concentrate heat and reduce heat loss.
Since the solar radiation is highly instable, the Stirling engine does not meet operation power requirement when the solar radiation is insufficient or absent. Therefore, an additional heat source is in need, which can be realized by combining the fuel gas heating with solar heating. Researches show that fuel gas temperature is usually below 1000° C. and the particle content is low, so the convective heat transfer mode dominates, and the radiation heat transfer accounts for about 31% of the total heat transfer. There are plenty of researches focusing on enhancement of the convective heat transfer between fuel gas and heat pipe to improve performance of the Stirling engine. The traditional heaters of the Stirling engine must have sufficient heat transfer area to completely heat the working gas. This indicates that the heater of the Stirling engine has a relatively large dead volume which affects the efficiency of the Stirling engine significantly. Realizing rapid heat transfer of part of the working gas in the heater of the Stirling engine and reducing the dead volume of the heater of the Stirling engine will play a key role in improving the output power and cycle efficiency of the Stirling engine.
In the dish-Stirling solar thermal power generation system, the temperature of the focus point of solar energy is very high, which presents a huge challenge for the material of the heater of the Stirling engine. In general, the Stirling engine usually avoids high temperature energy, thereby reducing the overall thermal efficiency.